Leetspeak (also Leetspeak or leet) originated as a cipher used by hackers to disguise their conversations online. The "language" began as a method of substituting ASCII characters for certain letters or numbers but has evolved to encompass various online jargon and portions of the videogame lexicon.
The term "leet" derives from the word "elite," a term used to describe highly skilled, usually high-profile, internet users and hackers. In the early stages of the internet many users were confused by leet's substitutions (such as the use of a "3" in place of an "E" — "l33t"). Today these types of substitutions are more nostalgic than cryptic and modern leet has been adopted by players of multiplayer videogames and MMOs.
The players of these games have a language all their own, using strings of the following acronyms and terms to form almost unintelligible sentences. To the uninitiated, a conversation on the World of Warcraft forums may seem more like code than true leet ever did. The roots of the modern usage can still be seen in words such as pr0n.
Leet became popular with online gamers as a means of effective shorthand to communicate while playing. With the spread in popularity of these videogames, however, the language has evolved into a form of ironic slang. Where once terms were used to shorten expressions — BRB = be right back — the recent trend is to extend the acronyms and "abbreviations" to the point of almost absurdity. LOL (laugh out loud) is now replaced in many uses by lollerskates, lollercats, lolomgwtfbbq, etc., much longer and unnecessary terms. The advent of programs and services that allow gamers to talk to each other using microphones has aided this trend as many previously text-only terms and expressions are now vocalized.